An ultra-compact, high-performance, multi-laser, many-parameter, bandwidth-selective flow cytometer is the expected result of the research and development proposed here. The cellular analysis typically carried out by a device of this type, through the use of lasers and photon detectors, will be moved to a whole new level of capability with the research detailed in this proposal. Specifically, revolutionary developments in the basic components of the cytometer: the focusing optics, the laser-interrogation system, and the photon-detection systems are proposed based upon several exciting advancements in these critical areas. Proposed research in optics will develop a sophisticated laser-focusing aperture that can be used with new powerful and compact solid-state lasers in order to increase the number of lasers used in a many-parameter, flow-cytometer system. State-of-the-art research in miniature, solid-state photon detectors will result in highly sensitive, silicon photodetectors, or avalanche photodiodes, that can be adapted for use in flow cytometers. These photon detectors will be used to replace conventional, cumbersome photomultiplier tubes. The current widespread use of flow cytometers as a method of diagnosing disease, especially cancer, through cell population analysis will benefit highly from the increase in sensitivity and capability provided by development of the high-performance device proposed here. Commercially, flow cytometers have wide market acceptance for use as core diagnostic devices in pathology and immunology departments in many hospitals across the United States. Since the market is established for these devices, our high-performance, extremely compact device should find broad acceptance and provide immediate technological improvement in the diagnosis and science carried out with flow cytometers.